1. Field of the Invention
The present invention relates to a push-button switch turned on and off by opening and closing a vehicle door, configured to turn a vehicle interior light or the like on and off, and secured to a vehicle body.
2. Description of the Related Art
Examples of known push-button switches for turning an interior light on and off in response to the opening and closing of a vehicle door include those disclosed in Japanese Unexamined Utility Model Registration Application Publications Nos. 5-15249 and 5-23365. A push-button switch disclosed in either of these publications includes a fixed member having a first fixed contact strip (negative side) and a second fixed contact strip (positive side) that are internally disposed on opposite sides, a control member biased by a spring from the fixed member while allowing engaging claws thereof to be engaged with holes of the fixed member so as to prevent the control member from being protruded by the biasing force of the spring from a desired position in the fixed member, and a movable contact strip arranged inside the control member and electrically short-circuiting the first and second fixed contact strips while being biased by the spring.
In the push-button switch configured as described above, when a vehicle door is closed, the movable contact strip is held in contact with the second fixed contact strip, as the control member is pressed with a side portion of the door against the biasing force of the spring. However, since the movable contact strip is isolated from the first fixed contact strip, the push-button switch is turned off, which means that an interior light is turned off. When in this state the door is opened, the control member is protruded by the biasing force of the spring. This allows the movable contact strip to be positioned between the first and second fixed contact strips, the push-button switch to be turned on, and the interior light to be turned on.
In general, small vehicles are equipped with a 12-volt battery, while heavy vehicles and diesel vehicles are equipped with a 24-volt battery or a 42-volt battery. Recently, there is a move to incorporate a 24-volt battery also into small vehicles. This is because the use of a high-voltage battery enables the use of thin and small-capacity wires in a wire harness and thus contributes to reduced vehicle weight. However, while the use of a 12-volt battery poses no problem, the use of a battery of 24 volts or more in a vehicle with the above-described push-button switch poses some problems.
Specifically, it is known that when the battery voltage is 15 volts or higher and a push-button switch is turned off, a spark occurs between a movable contact strip and a fixed contact strip at the moment when the movable contact strip is isolated from the fixed contact strip. In the known push-button switch described above, a spark does not occur between the second fixed contact strip connected to the positive terminal of the battery and the movable contact strip, which are always slidably in contact with each other. However, a spark occurs between the first fixed contact strip and the movable contact strip, as the movable contact strip is isolated from the first fixed contact strip.
Such an occurrence of a spark causes darkening of a contact portion where the movable contact strip comes into contact with the first fixed contact strip, results in poor contact, and causes the first fixed contact strip and movable contact strip to be damaged, cut, and become unusable.